Progressive tenses are compound tenses that express actions viewed as being in progress. In English, this tense would be constructed in the following way, the auxiliary verb being "to be".
|TO BE |
|present tense ||I am||+||running.|
|past tense||I was||+||running.|
|future tense ||I will be||+||running.|
The construction of the Spanish progressive tenses follows the same structure. It's the conjugated auxiliary verb ("estar" = to be) + the gerund.
|present tense ||Estoy||+||corriendo.|
|imperfect tense (past) ||Estaba||+||corriendo.|
The gerund in Spanish, like in English, gives the progressive tenses their progressive nature. In the English sentence "I am running", running is the gerund; gerunds in English are essentially any words ending in "-ing". Spanish gerunds also have a common ending: "-ndo". Here are a few examples in both English and Spanish.
|English gerund (-ing)||Spanish gerund (-ndo)|
To form the gerund in Spanish, you remove the infinitive endings (-ar, -er, -ir) and add -ando to the stem of the -ar words and -iendo to the stem of for the -er and -ir verbs. For example: